It is known in the art relating to internal combustion engines, especially where the cylinder heads or valve bodies are formed of aluminum or other relatively soft material, to provide separate valve seat inserts of a harder material, such as iron or steel. These form long wearing and serviceable seats for engagement by poppet valves in controlling access to the associated engine cylinders.
In order to retain such an insert in place, the cylinder head, cylinder block or other valve body, is generally provided with a cylindrical recess into which the harder insert is shrink, or press, fitted or a combination of both. To assure retention, the insert is generally shorter than the recess so that a portion of the recess wall extends beyond the insert. This portion is not subject to the direct stresses of the press or shrink fitting and, thus, remains unexpanded, thereby acting to positively retain the insert in its installed position.
We have found, however, that the stepped configuration of the insert and the adjacent protruding portion of the recess forms an impediment to gas flow through the open valve, which it is desired to avoid.